Or at least that's how it felt. The past few weeks have been incredibly tumultuous, sleepless, and beyond interesting. It is as if AMD and NVIDIA just started pulling out hardware and throwing it at eachother while we stood in the middle getting pegged with graphics cards. And we weren't just hit with new architectures and unexpected die shrinks, but new drivers left and right.

And now we have the other thing we've been working on since we finished GT200: RV770 in all it's glory. This includes the 4850 whose performance we have already seen and the Radeon HD 4870: the teraflop card that falls further short of hitting its theoretical performance than NVIDIA did with GT200. But theoretical performance isn't reality, and nothing can be done if every instruction is a multiply-add or combination of a multiply-add and a multiply, so while marketing loves to trot out big numbers we quite prefer real-world testing with games people will actually play on this hardware.

But before we get to performance, and as usual, we will want to take as deep a look into this architecture as possible. We won't be able to go as deep with RV770 as we could with GT200, as we had access to a lot of information both from NVIDIA and from outside NVIDIA that allowed us to learn more about their architecture. At the same time, we still know barely anything about the real design of either NVIDIA or AMD's hardware as they prefer to hold their cards very close.

This won't work long term, however. As we push toward moving compute intensive applications to the GPU, developers will not just want -- they will need low level architectural information. It is impossible to properly optimize code for an architecture when you don't know exact details about timing, latency, cache sizes, register files, resource sharing, and the like. While, this generation, we have decidedly more information from NVIDIA on how to properly program their architecture, we still need more from both AMD and NVIDIA.

And Now, the Rest of the Story

Last week was a weird teaser - we gave you the goods, without explaining what they were.

By now you know that the Radeon HD 4850 is the best buy at $199, but today we're able to tell you much about its inner workings as well as introduce its faster, more expensive sibling: the Radeon HD 4870.

ATI Radeon HD 4870

ATI Radeon HD 4850

ATI Radeon HD 3870

Stream Processors

800

800

320

Texture Units

40

40

16

ROPs

16

16

16

Core Clock

750MHz

625MHz

775MHz+

Memory Clock

900MHz (3600MHz data rate) GDDR5

993MHz (1986MHz data rate) GDDR3

1125MHz (2250MHz data rate) GDDR4

Memory Bus Width

256-bit

256-bit

256-bit

Frame Buffer

512MB

512MB

512MB

Transistor Count

956M

956M

666M

Manufacturing Process

TSMC 55nm

TSMC 55nm

TSMC 55nm

Price Point

$299

$199

$199

Priced at $299 the Radeon HD 4870 is clocked 20% higher and has 81% more memory bandwidth than the Radeon HD 4850. The GPU clock speed improvement is simply due to better cooling as the 4870 ships with a two-slot cooler. The memory bandwidth improvement is due to the Radeon HD 4870 using GDDR5 memory instead of GDDR3 used on the 4850 (and GDDR4 for 3870); the result is a data rate equal to 4x the memory clock speed or 3.6Gbps. The Radeon HD 4870 and 4850 both use a 256-bit memory bus like the 3870 before it (as well as NVIDIA's competing GeForce 9800 GTX), but total memory bandwidth on the 4870 ends up being 115.2GB/s thanks to the use of GDDR5. Note that this is more memory bandwidth than the GeForce GTX 260 which has a much wider 448-bit memory bus, but uses GDDR3 devices.

NVIDIA GeForce GTX 280

NVIDIA GeForce GTX 260

NVIDIA GeForce 9800 GTX

ATI Radeon HD 4870

ATI Radeon HD 4850

ATI Radeon HD 3870

Memory Size

1GB

896MB

512MB

512MB

512MB

512MB

Memory Technology

GDDR3

GDDR3

GDDR3

GDDR5

GDDR3

GDDR4

Memory Bus Width

512-bit

448-bit

256-bit

256-bit

256-bit

256-bit

Memory Clock

1107MHz

999MHz

1100MHz

900MHz

993MHz

1125MHz

Memory Data Rate

2.2Gbps

2.0Gbps

2.22Gbps

3.6Gbps

1.99Gbps

2.25Gbps

Memory Bandwidth

141.7GB/s

111.9GB/s

70.4GB/s

115.2GB/s

63.6GB/s

72.0GB/s

The use of GDDR5 enabled AMD to deliver GeForce GTX 260 class memory bandwidth, but without the pin-count and expense of a 448-bit memory interface. GDDR5 actually implements a number of Rambus-like routing and signaling technologies while still remaining a parallel based memory technology, the result is something that appears to deliver tremendous bandwidth per pin in a reliable, high volume solution.

AMD most likely took a risk on bringing GDDR5 to market this early and we do expect NVIDIA to follow suit, AMD is simply enjoying the benefits of jumping on the GDDR5 bandwagon early and getting it right, at least it seems that way. It wouldn't be too far fetched to imagine a 55nm GT200 die shrink with a 256-bit GDDR5 memory interface, it should allow NVIDIA to drop the price down to the $300 level (at least for the GTX 260).

As we mentioned in our Radeon HD 4850 Preview, both the Radeon HD 4870 and 4850 now support 8-channel LPCM audio output over HDMI. AMD just sent over 8-channel LPCM drivers for the Radeon HD 4870 so we'll be testing this functionality shortly. As we mentioned in our 4850 preview:

"All of AMD's Radeon HD graphics cards have shipped with their own audio codec, but the Radeon HD 4800 series of cards finally adds support for 8-channel LPCM output over HDMI. This is a huge deal for HTPC enthusiasts because now you can output 8-channel audio over HDMI in a motherboard agnostic solution. We still don't have support for bitstreaming TrueHD/DTS-HD MA and most likely won't anytime this year from a GPU alone, but there are some other solutions in the works for 2008."

The Radeon HD 4870 is scheduled for widespread availability in early July, although AMD tells us that some cards are already in the channel. Given that the 4870 relies on a new memory technology, we aren't sure how confident we can be that it will be as widely available as the Radeon HD 4850 has been thus far. Keep an eye out but so far the 4850 has been shipping without any issues at $199 or below, so as long as AMD can get cards in retailers' hands we expect the 4870 to hit its $299 price point.

Post Your Comment

173 Comments

i don't understand what you mean by raw numbers ... these are the numbers we got in our tests ...

we can't do crossfire on the nvidia board we tested and we can't do sli on the intel board we tested ...

we do have another option (skulltrail) but people seemed not to like that we went there ... and it was a pain in the ass to test with. plus fb-dimm performance leaves something to be desired.

in any case, without testing every solution in two different platforms we did the best we could in the time we had. it might be interesting to look at testing single card performance in two different platforms for all cards, but that will have to be a separate article and would be way to tough to do for a launch. Reply

In Bioshock in the multiGPU section the SLI 9800GTX+ seems to fall down on the job. In all other benches this SLI beats out the GTX 280 easily, here it fails miserably. While even the SLI 8800GT beats the GTX 280. Methinks something's wrong here. Reply

Egg's got them for 309.99. I'm gonna run 2 4870s in CF. I planned on using a P45 board but I am wondering if the P45s X8 per card will bottleneck the bandwidth and if I should go with an X48 board instead? When I research CF all I seem to find is "losing any bandwidth at X8 versus X16 is "debateable". What I'm thinking is that 8 pipelines can handle 4GBs so if I look at the 4870s 3.6 Gbs of memory bandwidth then X8 should be able to handle the 4870 without any performance hits. It that correct or am I all wet? Reply

I contacted ATI and they said I was correct. A P45 board only running X8 per card in CF will bottleneck the massive DDR5 bandwidth of the 4870s. If you're gonna CF 2 4870s use an X38 or X48 board. Reply

I created an account just to say how awesome this article was. It was really nice to see all the technical details laid out and compared to the competition. I was lucky to get in on that $150 hd4850 price at best buy last week and I am hoping the future drivers with improve performance even more. Please keep up the good work on these articles!!! Reply

and yes a lot of posters are reading way too much into it "you're biased waaa waaa boo hoo"

just get the facts from the article (thats what the charts and graphs are for) and then make your decision, if you cant do simple math and come to the conclusion yourself that the $300 card is a better buy than the $650 then you deserve to get ripped off. Reply

a very important comparison is missing. for those who want to go in for a multi-GPU setup, the 260 SLI vs 4870 CF is a very important consideration since SLI scaling has always been better than CF, and the 260 scales very very well.

in that case, if nvidia responds by reducing the price on the 260, the 260 SLI could be the real winner here. but sadly there were no 260 SLI benches.